Volcanos: Chapter 5

10-17-11

Volcano

• A volcano is a week spot in the crust where molten material, or magma, comes to the surface

Magma

• Magma is a molten mixture of rock-forming substances, gases, and water from the mantle

• When magma reaches the surface it is called LAVA

LAVA

• Lava is magma that has reached the surface/

• After lava has cooled it forms a solid rock.

• Lava that is released during volcanic activity builds up Earth’s surface.

Volcanoes and Plate Boundaries

• Observe figure 2 on page 147.

• Notice how volcanoes occur in belts that extend across continents and oceans.

• One major volcanic belt is called the Ring of Fire, formed by the many volcanoes that rim the pacific ocean.

• At plate boundaries, huge pieces of the crust diverge or converge.

• As a result, the crust often fractures and then allow magma to reach the surface.

• Most volcanoes form along diverging or converging plates.

Diverging Boundaries

• Volcanoes form along the mid-ocean ridges which mark diverging plate boundaries.

• Along the rift valley, lava pours out of cracks on the ocean floor, eventually building new mountains.

Converging Boundaries

• Many volcanoes form near converging plate boundaries where oceanic plates return to the mantle (subduction).

• Some of the rocks above the subductive plates melts and forms magma. Eventually the magma breaks through the ocean floor creating volcanoes.

Island Arcs

• When a string of islands are created, this creates an Island Arc. The curve of an Island arc echoes the curve of its deep-ocean trench.

• A volcano can also be formed where an oceanic plate is subducted beneath a continental plate.

Hot Spot Volcanoes

• Some volcanoes result from hot spots in Earth’s mantle.

• A hot spot is an area where material deep from within the mantle rises and then melts, forming magma.

• A volcano forms above a hot spot when magma erupts through the crust and reaches the surface.